Integrated services digital networks (ISDN) allow users of a telephone network to exchange both voice signals and data in digital form rather than analog form. This is a global telecommunication service that uses digital transmission and switching technology to support both voice and data communication over the same twisted pair, and provide end-to-end digital connectivity. Telecommunication networks currently employ both conventional (i.e. analog) terminal equipment (TE), e.g., user premises device that serves as a data source, data sink, or both, and ISDN (digital) terminals.
The architecture of these telecommunication networks becomes more complicated as the distance between the TEs and the ISDN terminals increase. The complex configuration of these networks require several types of equipment to be inserted between the ISDN switch and a multiplexer that serves to bundle multiple signals into a suitable format for transmitting over a single communications channel. To better explain such complexity, the typical architecture of current telecommunication networks is described below.
As shown in FIG. 1, the network architecture for a private ISDN local area network (LAN) user access 10 typically uses a network terminal (NT) 11 as an ISDN switch. An ISDN switch is generally an interface that connects ISDN wire pairs. An example of an ISDN switch is a Private Branch Exchange (PBX). The NT 11 connects a 2-wire pair digital subscribe line (U-interface) from the exchange and converts it to a 4-wire pair (S interface). The
NT 11 provides 4-wire S-interfaces (2B+D) 12 to interconnect multiple TEs 13 to form the LAN 10. Examples of a TE 13 are ISDN user premises devices such as ISDN telephones, data terminals, terminal adapters, etc. This network configuration 10, however, is only applicable if the distance between the NT 11 and the TE 13 is less that 1 km.
FIG. 2a illustrates a private ISDN LAN user access 20 where the distance between the ISDN switch 15 and the S/U converter 16 is greater than 1 km but less than 5 km. The network architecture of an ISDN LAN user access 20 at this distance typically uses an ISDN switch 15 that provides U-interfaces 14 instead of S-interfaces. It is also typical for the ISDN switch to assume the role of a line terminator (LT) 15 at the interface. A U-interface is a twisted pair subscriber loop that connects the Network Termination reference point to the ISDN network. Under U.S. regulations, a U-interface also marks the line of demarcation between customer-owned equipment and the public network. This network architecture 20 also requires S/U interface converters 16, each assuming the role of an NT, to interface with TEs 13.
FIG. 2b illustrates an alternative architecture to network 20 that may be used when the network architecture of a private ISDN LAN user access 30 does not contain an ISDN switch that provides a U-interface. Here, inserting S/U interface converters 17, each assuming the role of an LT, between S/U converters 16 and ISDN switch 9 solves the problem.
FIG. 3 illustrates network architecture for wide area networks (WAN) at distances greater than 5 km. Here, a U-interface 14 can be considered at the last kilometer, prior to the WAN network 41. At S-interface 12, a TE 13 is connected to an NT 16, acting as an S/U interface, to a multiplexer comprising an LT 18 and a MUX 19. In this arrangement, two S/U interface converters, one as an NT 16 and one as an LT 42, are employed in a manner similar to the network configuration of FIG. 2b. While an NT mode S/U interface converter 16 is readily available, an LT mode interface S/U converter 42 is not.
As provided in the Mitel MT8930C Subscriber Network Interface Circuit data sheet, FIG. 8 illustrates an example of an NT mode S/U interface converter. As shown in FIG. 8, components MT8930C subscriber network interface circuit (SNIC), MT8910-1 digital subscriber line interface circuit (DSLIC), and a Microprocessor form a conventional NT mode S/U interface converter. The Microprocessor initializes and configures the registers of the SNIC MT8930C and DSLIC MT8910-1 to NT mode. Upon initialization and configuration, the DSLIC MT8910-1 operates in a slave mode and sources timing signals from the U-interface. The DSLIC MT8910-1 then outputs the U-interface timing signals to the SNIC MT8930C. After receiving the U-interface timing signals, the SNIC MT8930C outputs the U-interface timing signals to the S-interface, acting as a master the S-interface. The conventional S/U interface converter of FIG. 8 is only operable in the NT mode and does not provide an option of operating in the LT mode.
An attempt to overcome this problem is to use an ISDN switch 9 that assumes the role of an LT with U-interface 17 as shown in FIG. 2b. However, for ISDN switches used in a LAN environment existing only with S-interfaces, it will not be possible to connect to a WAN network unless U-interface subscriber line cards 42, acting as LTs, are designed and implemented for each private ISDN switch 43. This approach is not economical because multiple separate line cards are required.
Another attempt to overcome this problem is to design an S-interface line card for the multiplexer 18, 19. In both cases, however, time and effort is required to design new subscriber interface cards, and the cost of implementing such design is high.
One object of the present invention is to provide an ISDN S/U interface converter that overcomes the above and other disadvantages of conventional ISDN S/U converters.
Another object of the present invention is to provide an ISDN S/U interface converter that shares a common hardware platform with hardware jumper configurations.
An additional object of the present invention is to provide an ISDN S/U interface converter that shares a common hardware platform with hardware jumper configurations and that can select the signal path and running firmware to perform the role as an LT or NT.
An even further object of the present invention is to provide an ISDN S/U interface converter that has a selectable and reversible direction of sync flow.
A still further object of the present invention is to provide an ISDN S/U interface converter that has a selectable and reversible direction of sync flow over a common path, with a common synchronization circuit, common control, and common data bas.
Another object of the present invention is to provide an ISDN S/U interface converter that provides an arrangement of such selectably configured structures together with links to local networks and long distance networks.
An additional object of the present invention is to provide an ISDN S/U interface converter that provides convenience, both economically and systematically, for a system integrator to use and maintain only one type of equipment.
Another object of the present invention is to provide an ISDN S/U interface converter that allows connectivity to WAN networks for switches used in LAN environments existing only with S-interface connections.